Create a sail with cloth and curves acting as softbodies
I'd suggest ditching the curves all together. They make the simulation hard to achieve, don't add anything to the scene realism and only add complexity to the simulation.



Just subdivide your sail enough for the desired level of detail. Add a new Vertex Group and assign it only to the 3 corner vertex (or any other undeformable parts that may be attached to cables).



Add a Cloth physics type to the sail, and pick the group for the Pinning option.

Then add a new Force Fied type object of the Wind kind, point it towards the sail and adjust its speed and turbulence.